We plan to use mice and to study the changes in immunological capacity with aging. Particular emphasis will be made to the contribution of T-lymphocytes ahd B-lymphocytes in response to haptens on self-carriers and on foreign carriers. Mice of different ages will have their lymphoid cells cultured in vitro (primary) or in vivo (primary) and responses will be tested in vivo or with secondary in vitro challenge. Antibody titers to haptens can be studied in vivo, and cellular proliferative responses of both T- and B-cells in vitro. Adoptive transfer will be used. Aged lymphocytes and aged autologous carriers will be compared with young lymphocytes and carriers.